# COMP1110 Lab 7
## Before the Lab
* Complete week 8 of your personal journal, commit and push at least 5 minutes prior to the start of your lab.
* Make sure you’ve covered module [**X01**](https://cs.anu.edu.au/courses/comp1110/lectures/javafx/) and [**X02**](https://cs.anu.edu.au/courses/comp1110/lectures/javafx/#x2) (JavaFX).
## Purpose
In this lab you will extend the your Board program from Lab 6 to include drag-and-drop.
**It is essential that you complete this lab and have a tutor mark it off during the lab**.
## JavaFX Drag and Drop
1. **Create an inner class**
Create a new inner class `DraggableTriangle`, that extends your inner class `Triangle`.
2. **Add a constructor**
Add a constructor to your new inner class with the following signature: `DraggableTriangle(double x, double y, double size, Board board)`. Ensure that this constructor calls its parent constructor (`super(x, y, size)`), and then sets the fill color to`RED`.
3. **Add a new field**
Add a private instance field `board` to your `DraggableTriangle` inner class and initialize it in the constructor (i.e. `this.board = board;`).
4. **Create a draggable triangle**
Within the `start()` method of your `Board` class, create a new `DraggableTriangle` of size 200, centered at (300, 260), and with the board (i.e. `this`) passed as the fourth argument to the constructor. Remember to add the draggable triangle to your root group.
5. **Make the inner class draggable**
Make the inner class `DraggableTriangle` draggable. The approach here is to identify how much the mouse has moved (by comparing its current position to its last position), and then move the triangle by that same amount.
* Add two private instances fields to the inner class, both doubles, to track the location of the mouse as the object is dragged. Call them `mousex` and `mousey`.
* Remember where the mouse is when it is first pressed, and ensure your triangle remains visible. Do this within the constructor by establishing a handler for mouse presses. You need to add code to the constructor for `DraggableTriangle` that looks something like this:
““Java
this.setOnMousePressed(event -> {
.. your code here ..
});
““
* Your code should store the current mouse x and y positions in the private fields (e.g. `mousex = event.getSceneX()`, etc), and should ensure the draggable triangle is not covered by other nodes in the scene (call `toFront()` to ensure this).
* Move the triangle as the mouse is dragged using a handler via `setOnMouseDragged()` in much the same way as you did for `setOnMousePressed()` in the previous step. In that code, find out how much the mouse has moved (e.g. use `event.getSceneX() – mousex`), and change the location of the triangle by the same amount (use `setLayoutX()`, etc). Then remember the new mouse location (updating `mousex` and `mousey`), so that it is all ready for the next time the event occurs.
You should now be able to drag the red triagle around.
6. **Add a distance calculator**
Add a method to your inner class `Triangle` with signature `private double distance(double x, double y)` that returns the euclidian distance from the center of the triangle to the point (x,y), (using Pythagoras’ theorem :-).
7. **Find the nearest triangle**
Add an instance method to your `Board` class that allows you to find the nearest triangle to a given point, it should have a signature something like `Triangle findNearestTriangle(double x, double y)`. You can do this by simply iterating over all the triangles in your `ArrayList
8. **Highlight the nearest**
Highlight the triangle nearest the draggable triangle:
* Add a new field to your `Board` class that allows you to remember a ‘highlighted’ triangle, and initialize the field to `null` (e.g. `Triangle highlighted = null;`).
* Add a method `void highlightNearestTriangle(double x, double y)` that highlights the triangle nearest a point (`x`, `y`). This method should first un-highlight the currently highlighted triangle (if there is one), by filling it with `LIGHTGREY`. It should then set the variable `highlighted` to be equal to the nearest triangle to (`x`, `y`), and then it should set the fill color of the highlighted triangle to `GREEN` (or whatever color you prefer).
* Add a line to your `setOnMouseDragged()` event in the constructor of `DraggableTriangle` that calls `board.highlightNearestTriangle()` with the location of your draggable triangle as arguments. You should now find that as you drag your red triangle around, the triangle nearest it is highlighted green.
9. **Snap to nearest triangle**
Finally, make your draggable triangle snap to the nearest triangle. To do this, add a handler for mouse release (use `setOnMouseReleased()`, just like you did for `setOnMousePressed()` and `setOnMouseDragged()`). In that code, find the nearest triangle to your draggable triangle, and then make the location and orientation of the draggable triangle be the same as that of the nearest triangle (using `setRotate()`, `getRotate()`, `setLayoutX()`, etc.).
10. **Finish off**
Commit and push your work, close the relevant issue (#19), and notify your tutor.
## Extension: Hashing
**Create a hash program**
Using the lecture code from C03 as a template:
* Read the data from `assets\us_postal_codes.txt`. Each line contains a postal code,town name, state name, state code,county name, latitude and longitude.
Then:
Imagine you are in charge of the entire US postal service, and you have only 50 delivery officers to cover the entire country (40933 zip codes).
You want to give each person a roughly equal amount of work (imagine each post code has the same amount of mail).
Create a hash function that will:
1. Split the work as evenly as possible (imagine that each post code has the same amount of mail)
2. Minimise the travel each person does as much as possible. Imagine that each person starts at any one of their zip codes, and avoid them having to travel across the country.
You can test 1. by running the program and checking the histogram of results to see if the hash function is even.
How many ways can you do this?
## Work on your group assignment
Use any spare time to work on your group assignment.